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Homework Help: Stacked Blocks Question

  1. Feb 14, 2010 #1
    1. The problem statement, all variables and given/known data

    There are two blocks, the bottom block with a mass of 2kg and a block with mass of 1 kg stacked on top of it. Block on bottom is being pulled to the right by a tension force of 20 N. The top block is connected to the left wall by a rope. The coefficients of kinetic friction are .40 on bottom and top of the 2kg block.

    Q1) What is the tension in the rope holding block of 1kg
    Q2) what is the acceleration of block of 2kg

    2. Relevant equations

    Newtons 2nd/3rd law.

    3. The attempt at a solution

    For part 1, i have attempted to set Fnet(2) = 20N (tension)- Ffriction(2 on ground) - Ffriction(1 on 2)
    and then set Fnet(1) = 0 = -T + Ffriction(1 on 2)

    I cannot find how to relate them. I know that the top block should stay stationary while the bottom block moves away, but I dont know what masses to use to calculate the normal forces.

    I figure if I can get guided to the answer for part 1, part 2 might be solvable. Thanks for your help.
  2. jcsd
  3. Feb 14, 2010 #2


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    Homework Helper

    Write the equations for the vertical force components. From those, you get the normal forces. Multiplying the normal forces with the coefficient of friction, the forces of friction are obtained.

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